A signal-on ratiometric fluorometric heparin assay based on the direct interaction between amino-modified carbon dots and DNA.

Amino-modified carbon dots (C-dots) with positively charged surface were prepared. They display strong blue fluorescence and are shown to act as quenchers of the green fluorescence of FAM-labeled ssDNA such as the F-probe used in this work that was immobilized on the C-dots. On the addition of highly negatively charged heparin (Hep), it will interact with the C-dots and displace the F-probe from C-dots.

Ratiometric electrochemical immunoassay based on internal reference value for reproducible and sensitive detection of tumor marker.

A ratiometric assay in an electrochemical immunosensor for tumor marker, herein carcinoembryonic antigen (CEA) was chosen as a model analyte, was developed to improve simplicity and accuracy. The immunosensor was fabricated via the simple expedient way of using Polythionine-gold (PTh-Au) as electrode modified material to be an internal reference signal and K3[Fe(CN)6] in electrolyte as an indicator signal. When the CEA was fixed on the modified electrode via immunoreaction, only the indicator signal sensitively altered; by contrast, the internal reference signal of PTh-Au remained constant at a suitable pH of the electrolyte.